Leon was searching for yet another terrorist using bioweapons to try to end the world. He was walking through a facility when he got attacked by a mercenary, a man hired by the scientist he was after.

Leon fought, but he was exhausted, having been killing BOWs for the past few hours.

Just as it looked like he might lose to the mercenary, a shot rang out, exploding the man's head. His dead body dropped on Leon who pushed him off, turning to look at who saved him. It was you: his enemy.